Conventional and unconventional virus-like agents establish persistent infections in the CNS of man and animals and may play a role in chronic degenerative diseases such as multiple sclerosis (MS) and Alzheimer's disease (AD). The major objective of this proposal is to determine with what frequency viral genes are deposited in the human CNS and the relationship of such a residue of infections early in life to MS and AD. The studies will continue to depend on refined and sensitive methods of in situ hybridization which are capable of detecting a single copy of viral genome.